We wish to study the molecular events underlying the initiation of mitosis in mammalian cells. Our previous studies have demonstrated the existence of a protein(s) found in mitotic mammalian cells that reproducibly induces the initiation of meiosis when injected into X. laevis oocytes. We have named this protein MIP for mitotic inducing protein(s). The bulk of our work now will be to purify this protein and delineate its physico-chemical characteristics. We will use standard techniques of protein chemistry in our purification scheme; this includes molecular sieve chromatography, ion exchange and affinity chromatography, and isoelectric focusing. The purification will be based on a bioassay for the capacity to induce meiotic maturation in immature oocytes. Concurrent with this purification, we intend to initiate other studies to probe the nature of MIP. Studies to investigate the role of phosphorylation in induction and/or cessation of the activity of MIP will be undertaken. We will also attempt to develop a bioassay based on the ability of MIP to induce mitotic-like changes in somatic cells. We will carry out a pilot study to assess whether the message RNA coding for MIP can be detected. Finally, we will attempt to demonstrate and purify factors from interphase cells that inactivate MIP at the end of mitosis. These studies provide a biochemical approach for the elucidation of the nature of the events underlying a critical stage in the life of every eukaryotic cell.